A runaway train went through six stops on a 13-minute journey on the Tube on Friday with other Underground trains having to be cleared out of its path.
The unmanned engineering train, used for maintenance, began to move southbound from Archway station on the Northern line.
London Underground (LU) staff took an operational decision to let the train continue and diverted trains on to another branch of the Northern line while clearing trains from the Charing Cross branch on which the runaway train had been diverted.
The train eventually came to a stand at Warren Street station. LU and the Rail Accident Investigation Bureau have launched an investigation into the incident and LU has suspended the use of all engineering trains of this type.
LU said the train had become defective at 5.25am today as it approached Archway. Engineers began to move the train northbound by coupling it to an out-of-service Northern line train.
The incident involved the suspension of the Northern line between Finchley Central and Archway and Camden Town to Kennington via Charing Cross - a suspension that was still in place by late morning.
